Color image recording materials have come to prevail over black-and-white image recording materials. They have found use in several applications, such as in ink jet recording, heat transfer recording, electrophotography, transfer type silver halide photographic materials, printing inks, recording pens, and color filters in displays, such as liquid crystal displays and plasma display panels, and solid-state image sensors, such as charge coupled device (CCD) image sensors.
These color image recording materials and color filters use colorants (dyes and pigments) of additive or subtractive primaries to implement full color reproduction or recording. Nevertheless, colorants having absorption characteristics suitable for favorable color reproduction and fastness against various conditions of use are not currently available.
Ink jet recording has rapidly become popular and will see further development because of low material cost, high speed, low noise, and ease of color recording. Fundamentally, ink jet recording is divided into a continuous method in which ink droplets are continuously allowed to fly and a drop-on-demand method in which ink droplets are made to fly upon image information signals. The mechanism of drop formation includes a piezoelectric system in which pressure is applied to ink by a piezoelectric element to eject ink droplets, a thermal system in which an air bubble is generated by heat to eject ink droplets, an acoustic system, and an electrostatic system in which ink droplets are sucked or ejected by an electrostatic force. Ink-jet inks include aqueous ink, oily ink, and solid ink (melting type).
Colorants used in ink-jet inks are required to have (1) good solubility or dispersibility in ink solvents, (2) capability of forming a high-density image, (3) satisfactory hues, (4) fastness against light, heat, and active gases in the environment (e.g., NOx, oxidizing gases such as ozone, SOx, etc.), (5) resistance against water or chemicals, (6) good fixability on media with minimized feathering, (7) stability in ink formulations, (8) nontoxicity, (9) high purity, and (10) inexpensiveness. It is extremely difficult to obtain colorants meeting all these requirements. In particular, colorants having both a favorable magenta hue and fastness to light and active gases in the environment, particularly oxidizing gases such as ozone, have been eagerly sought.
Coupling components for azo dyes that have been widely used include phenols, naphthols, and anilines. JP-A-11-209673 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) and Japanese Patent 3020660 disclose azo dyes obtained by using these coupling components, which have satisfactory hues but poor light fastness. Japanese Patent Application No. 2000-220649 proposed dyes with satisfactory hues and improved light fastness. However, all the colorants known by the literature are extremely unsatisfactory in fastness to oxidizing gases such as ozone.
In seeking for dyes with satisfactory fastness to oxidizing gases such as ozone, the present inventors have arrived at the idea of using a nitrogen-containing heterocyclic compound as a coupling component, dropping the idea of using the conventional coupling components such as phenols, naphthols, and anilines. Azo dyes made from an aminopyrazole diazo component and an aniline coupling component are disclosed in JP-A-55-161856, JP-A-61-36362, JP-A-61-152768, JP-A-6-145543, JP-A-7-224230, U.S. Pat. Nos. 4,650,861 and 4,301,070, and JP-W-11-504958 (The term “JP-W” as used herein means an “international patent application published in the Japanese national proceeding”). As stated above, none of the conventional techniques has succeeded in furnishing azo dyes satisfactory in both hue and fastness. Azo dyes comprising a pyridine coupling component are known as disclosed in JP-A-51-83631, JP-A-49-74718, JP-A-58-101158, JP-B-52-46230 (The term “JP-B” as used herein means an “examined Japanese patent application”), European Patent 23309, and German Patents 2719079, 2307444, 2513949, 2525505, and 2832020. Azo dyes comprising a pyrazole diazo component and a pyridine coupling component are utterly unknown.
Azo dyes composed of a pyrazole diazo component and an aniline coupling component have been synthesized according to the processes taught, e.g., in U.S. Pat. Nos. 3,336,285 and 3,639,384 and British Patent 1,566,985. The process of the U.S. Patents comprises diazotizing a 1-alkyl-4-cyano-5-aminopyrazole followed by coupling reaction to produce a 1-alkyl-4-cyanopyrazol-5-yl azo pigment. However, a diazonium salt used in the process is very labile, causing difficulty in obtaining dyes in high yield and with high purity through diazotization and coupling (see Weaver and Shuttleworth, Dyes and Pigments, vol. 3, p. 81 (1982)). 1-Alkyl-3-(secondary or tertiary alkyl)-4-cyanopyrazol-5-ylazo dyes synthesized by the process disclosed in JP-B-6-19036 have hues of short wavelengths and are unsatisfactory as magenta dyes.
The process proposed in British Patent 1,566,985 supra comprises subjecting a 1-alkyl-3-alkyl(or aryl)-4-halogeno-5-aminopyrazole and an aromatic coupling component to diazotization and coupling and substituting the halogen at the 4-position with —CN to synthesize a 1-alkyl-3-alkyl(or aryl)-4-cyanopyrazol-5-ylazo dye. Using a heavy metal cyanide, e.g., CuCN or Zn(CN)2, the process involves such issues as waste disposal and purification of produced dyes.
A process for producing an azo dye comprising a pyrazole diazo component and a pyridine coupling component with ease and in high yield is unknown. Known processes applicable to synthesis of the compound of the present invention have many drawbacks. In addition, introducing an arbitrary substituent to the amino group of the pyridine moiety of a dye compound represented by formula (I-H1) according to the invention has been often accompanied with heat elevation or has often involved a complicated reaction system which makes product isolation difficult. Moreover, it is unknown how to water-solubilize an azo dye comprising a pyrazole diazo component and a pyridine coupling component with ease and in high yield.